1. Field of the Invention
The present invention relates to an improved method for manufacturing a perpendicular magnetic recording medium.
Priority is claimed on Japanese Patent Application No. 2008-249627, filed Sep. 29, 2008, the content of which is incorporated herein by reference.
2. Description of Related Art
The recording density of hard disk devices (HDD), which are one type of magnetic recording and reproducing apparatus, is currently increasing at an annual rate of 50% or higher, and it is expected that this trend will continue in the future. Consequently, the development of magnetic recording heads, and the development of magnetic recording media suitable for high density recording is being advanced.
Currently, a magnetic recording medium that is installed in the commercially available magnetic recording and reproducing apparatus is a so-called perpendicular magnetic recording medium in which the axis of easy magnetization within a magnetic film is mainly oriented perpendicularly. In the perpendicular magnetic recording medium, even when recording density is increased, the effects of a demagnetizing field formed in the boundary region between recording bits are small and distinct bit boundaries are formed, thus enabling noise reduction. Furthermore, reduction in recording bit volume associated with the increase in recording density can be suppressed, and thus thermal stability can also be enhanced. Therefore, in recently years, a perpendicular magnetic recording medium has become of keen interest, and a medium structure suitable for perpendicular magnetic recording has been proposed.
In the meantime, in the conventionally magnetic recording media in which an in-plane recording system is employed, a texture processing has been conducted on the surface of a non-magnetic substrate before forming a magnetic layer or the like thereon. The texture processing refers to a processing in which a texture streak (fine irregularities) along the circumferential direction is formed on the surface of a non-magnetic substrate so that the medium surface has an adequate surface roughness and also that the magnetic recording medium is provided with the magnetic anisotropy along the circumferential direction. That is, when forming a magnetic layer on a disc substrate where fine texture streaks are present on the surface of a non-magnetic substrate, it has been known that electromagnetic conversion characteristics improve, as compared to the case where a magnetic layer is formed on a disc substrate where no texture streaks are present. This is because by conducting a texture processing on the surface of a disc substrate, the crystal orientation in the base layer and magnetic layer which are formed on the surface of this disc substrate improves. This enables enhancement of magnetic anisotropy of the magnetic layer and improvements in magnetic properties such as the resistance to thermal fluctuation.
The texture processing is conducted by supplying a polishing slurry to the surface of a disc substrate while rotating this disc substrate and pressing a running polishing tape onto the surface of the disc substrate (for example, refer to Patent Document 1, i.e. Japanese Unexamined Patent Application, First Publication No. 2004-178777 and Patent Document 2, i.e. Japanese Unexamined Patent Application, First Publication No. 2004-259417). In addition, as a polishing liquid, those in which diamond abrasive grains are dispersed in a dispersion medium have been used.
Moreover, in Patent Document 3, i.e. Japanese Unexamined Patent Application, First Publication No. 2008-108396, there is disclosed a method for manufacturing a perpendicular magnetic recording medium by which abnormal protrusions in the base layer formed of a Ni—P based alloy can be automatically removed while securing a flat surface with high accuracy for the base layer, and also adequate texture marks can be formed so that the magnetic orientation in the perpendicular direction is easily achieved without adversely affecting the magnetic orientation in the perpendicular magnetic recording medium.
On the other hand, in the manufacturing process of perpendicular magnetic recording media, no texture processing is generally conducted on a non-magnetic substrate and a non-magnetic substrate having a smooth surface is used. This is because if a magnetic film or the like is formed on the surface of a non-magnetic substrate when irregularities or scratches are present on the surface of the non-magnetic substrate, abnormal protrusions or the like are often formed at places where these irregularities or scratches are present. Accordingly, a substrate used for manufacturing a perpendicular magnetic recording medium is produced by undergoing a multitude of wrapping steps and polishing steps, and thus the surface thereof is satisfactorily smooth. However, after producing the substrate for a perpendicular magnetic recording medium, several days are required in many cases until the substrate is used for forming a magnetic film or the like thereon, and particles or the like are often adhered onto the surface of the substrate during that time. In addition, even higher smoothness is required for the surface of the substrate used for manufacturing a perpendicular magnetic recording medium, and demands for a polishing process which is capable of smoothing substrate surfaces have been increasing. Moreover, such polishing process is preferably conducted immediately prior to the formation of a magnetic film or the like on a substrate in order to reduce the extent of adherence of particles or the like onto the substrate as much as possible.
The present invention is made in order to solve the above-mentioned problems and provides a method for manufacturing a perpendicular magnetic recording medium that includes a step for forming a smooth substrate surface without generating abnormal protrusions or the like when forming a magnetic film or the like on the surface of the substrate.